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/**
 * Redirect CF7 After Submission
 *
 * Accepts 'custom_on_sent_ok' parameter in CF7 form additional settings. e.g.,
 * custom_on_sent_ok: http://example.com/thank-you
 */
add_action( 'wpcf7_mail_sent', 'custom_redirect_cf7_form' );
function custom_redirect_cf7_form( $wpcf7 ) {

  $on_sent_ok = $wpcf7->additional_setting('custom_on_sent_ok', false);

  if ( is_array( $on_sent_ok ) && count( $on_sent_ok ) > 0 ) {
    wp_redirect( trim( $on_sent_ok[0] ) );
    exit;
  }

}